Smelting furnaces are regularly provided with exhaust devices to reduce toxic emission and environmental loading. For example, an arc furnace is known from DE-AS 19 28 501 in which an exhaust line is provided at the furnace cover. The exhaust line has adjusting and throttle devices by which the exhaust device can be adjusted in accordance with the operating processes in the arc furnace, i.e. smelting, refining, alloying, and de-slagging. A portion of the flue gases occurring in the furnace flows through the burden or charge column in accordance with the thermal currents and is sucked out below the cover at a nominal negative pressure.
If scrap containing not only so-called solid or high-grade melting scrap but also an abundance of impurities, e.g. in the form of varnish, plastics, oils and grease, is melted in such an arc furnace these materials may reach the exhaust device as gas, vapor or dust. Costly after-treatment devices such as after-burning chambers with external heating, dust processing and dust detoxification systems are provided before it is possible to emit to the atmosphere the exhaust gases which are to be cleaned in a filter system. These after-treatment devices require a significant expenditure of energy and are thus uneconomical to operate.
A process and a device for thermal decontamination of filter dusts and other residual substances is known from DE-OS 38 27 086 in which the material is introduced into an induction heated crucible furnace for removing possible contents of dioxins and furans and for preventing a possible leaching of heavy metals contained therein. The dust is melted in this crucible furnace at temperatures of 1400 to 1600 degrees Celsius and the liquid phase is removed and quenched in a water bath. The forming gas phase is simultaneously guided along a high-temperature section of at least 1200 degrees Celsius and the exhaust gas is then shock-cooled via a spray cooler. In this process, the solids are separated off in a subsequently connected high-power dust separator. This process in addition to being costly has a disadvantage of first producing toxic dust prior to treatment.